package LeetCode;

public class LC_021_MergeTwoSortedLists {
    public static void main(String[] args) {

    }

    private ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        if (l1 == null) return l2;
        if (l2 == null) return l1;

        if (l1.val > l2.val) {
            l2.next = mergeTwoLists(l1, l2.next);
            return l2;
        } else {
            l1.next = mergeTwoLists(l1.next, l2);
            return l1;
        }
    }

    private ListNode mergeTwoLists_1(ListNode l1, ListNode l2) {
        if (l1 == null)
            return l2;
        if (l2 == null)
            return l1;

        ListNode cur;
        if (l1.val < l2.val) {
            cur = l1;
            l1 = l1.next;
        } else {
            cur = l2;
            l2 = l2.next;
        }

        ListNode fakeHead = new ListNode(-1);
        fakeHead.next = cur;

        while (l1 != null && l2 != null) {
            if (l1.val < l2.val) {
                cur.next = l1;
                cur = cur.next;
                l1 = l1.next;
            } else {
                cur.next = l2;
                cur = cur.next;
                l2 = l2.next;
            }
        }

        if (l1 != null)
            cur.next = l1;
        if (l2 != null)
            cur.next = l2;

        return fakeHead.next;
    }
}
